Introduction: The Meade MA 12mm Astrometric Eyepiece
(1.25” O.D.) functions as a multiple measuring device for
determining angular diameters and position angles of celestial
objects. It is also an excellent guiding eyepiece, used to
monitor a guide star through an off-axis guider or guide
telescope during long-exposure astrophotography.
The precision-etched glass reticle is illuminated by a
continuously variable-brightness red LED (Light Emitting
Diode), that can be dimmed to allow observations of very faint
objects. The eyepiece can be focused to match the user’s eye
diopter so that the scales of the reticle can be examined in
sharp focus.
Focusing the Eyepiece: To focus the reticle of the Astrometric
Eyepiece, turn the Eyelens Focuser (1, Fig. 1) of the eyepiece
clockwise or counterclockwise until the reticle scales are seen
at their sharpest.
Using the LED Illuminator: To turn on the illuminator, rotate
the illuminator control knob (3, Fig. 1) past the click stop.
Illumination brightness control is varied by further turning the
control knob. Turning clockwise increases the brightness of the
LED, while counterclockwise decreases the brightness. To turn
the illuminator off, turn the control knob all the way
counterclockwise until it is turned to the click stop.
Astrometric Reticle Scales: There are 4 reticle scales etched
into the glass reticle (Fig. 2) of the eyepiece that correspond to
the table below:
Scale Type Description
1 Linear Diameter 0 to 50 Units; Segmented
Scale in Single Units with
Circular Center Position
2 Semicircular Position 0 to 90 Degrees with
Angle Scale Circular Center Position
3 360° Position Angle Segmented in Units of 5°
Scale
4 Double Crossline/ Four Concentric Circles
Concentric Circle with Each Inner Circle
Guiding Scale Representing .5 Width,
.25 Width, and .10 Width
of the Outer Circle
Dimension, Bisected
with a Double Crossline
Determining Image Scale: An accurate determination of the
image scale for a given telescope can be accomplished by
making visual timings of a star as it drifts through the
Astrometric Eyepiece. To make the measurement follow these
steps:
1. Set up the telescope and insert the Astrometric Eyepiece
with the LED Illuminator turned on.
2. Check the collimation of the telescope (refer to the
telescope’s instruction manual). A collimated telescope
produces the best image possible.
3. Bring the telescope to a sharp focus.
4. Aim the telescope at or very near (within +/- 5°) the zenith
(perpendicular to the ground).
5. Turn off the telescope motor drive.
6. Rotate the Astrometric Eyepiece so that a star drifts along
(
i.e.
, parallel to) the Linear Diameter Scale (1, Fig. 2) of
the reticle.
7. Take three timings (in seconds) of a star as it crosses the
Linear Diameter Scale. Begin the timing as the star
crosses one edge of the scale and end the timing as the
star crosses the other edge of the scale.
8. Record the timings and average them.
With the timings recorded and averaged, an accurate
determination of the angular diameter of the sky that the Linear
Diameter Scale represents can be calculated. Stars at or near
the zenith move across the sky at 15 arc seconds per second
(sidereal rate). To determine the true angular diameter in arc
seconds, multiply the number of seconds of the averaged
timing of the scale by 15. This number represents the entire
length of the scale in arc seconds. To know the number of arc
seconds represented by each of the segments of the scale,
divide by 50. To know the value in arc minutes, divide arc
seconds by 60. To know the value in degrees, divide arc
seconds by 3600.
Example:
If the star takes 10 seconds to cross the entire length of the
scale:
seconds X 15 = angular diameter in arc-seconds
10 X 15 = 150 arc-secs angular diameter
arc-secs ÷ 60 = angular diameter in arc-minutes
150 ÷ 60 = 2.5 arc-mins angular diameter
arc-secs ÷ 3600 = field of view in degrees
150 ÷ 3600 = 0.041° angular diameter
Use the above techniques and formulas for making
measurements of any of the scales on the reticle of the
Astrometric Eyepiece. Repeat these steps if the Eyepiece is
used on a different setup (
e.g.
, used with a different diagonal,
a Barlow lens, etc.).
Knowing the measurements of the scales of the reticle, the
observer can take measurements to determine apparent
diameters or angular separations of celestial objects (
e.g.
,
planets, deep-sky objects, craters on the Moon, double stars,
etc.). Other measurements can be made, such as the periodic
error of the telescope’s drive system.
Operating Instructions
Meade®MA 12mm Astrometric Eyepiece
T
Fig. 1: MA 12mm Astrometric Eyepiece. (1) Eyelens
Focuser; (2) Red LED Illuminator with Continuously Variable
Brightness Control; (3) Brightness Control Knob.
1
2
3
MEADE MA
ASTROME
ILLUMINATED
Determining Position Angle: Position angle (PA) in
astronomical terms is the direction in the sky of one celestial
body with respect to another, measured from 0° to 360° in an
easterly direction from north. Position angles are used by
astronomers, for example, to give the position of a tail of a
comet with respect to the nucleus of the comet, or to measure
the position angle one component of a multiple star to another.
To make a position angle measurement, calibrate the
orientation of the 360° Position Angle Scale (3, Fig. 2) along the
east-west line of the sky by following these steps:
1. Set up the telescope and insert the Astrometric Eyepiece
with the LED illuminator turned on.
2. Check the collimation of the telescope (refer to the
telescope’s instruction manual). A collimated telescope
produces the best image possible.
3. Bring the telescope to a sharp focus.
4. Aim the telescope at or very near (within +/- 5°) the zenith
(perpendicular to the ground).
5. Turn off the drive of the telescope.
6. Release the set-screw of the eyepiece holder and rotate
the Astrometric Eyepiece within the eyepiece holder so
that a star drifts across the 90° mark of the Position Angle
Scale and then exits across the 270° mark.
7. Tighten the set-screw of the eyepiece holder to lock the
position.
Once the scale is successfully calibrated along the east-west
line of the sky, follow these steps to measure the position angle
of a celestial object:
1. Place the reference object (
e.g.
, primary component of a
comet nucleus) in the circular mark at the center of the
Linear Diameter Scale (1, Fig 2.).
2. Find the object that the position angle is measured for
(
e.g.
, discernable edge or center line of a comet’s jet or tail
that extends across the eyepiece field of view).
3. Read the position angle.
For example, if the nucleus of a comet is placed in the center
of the Linear Diameter Scale, and the center of the tail (the
object the PA measures for) is in-line with the first segment
after 300 on the Position Angle Scale, then the PA of the center
of the comet’s tail is 305°.
Important Note: The Position Angle Scale reads clockwise
from 0° to 360° as used through mirror-lens Cassegrain
telescopes (
e.g.
, Schmidt-Cassegrain, Maksutov-Cassegrain),
or refractors where a diagonal mirror/prism is being used. If the
Astrometric Eyepiece is being used without a diagonal prism or
through a Newtonian reflecting telescope, the position angle
reading should be reversed (
e.g.
, 90° translates to 270°)
.
If the PA of a double-star, or other closely spaced objects is to
be measured, use the Semicircular Position Angle Scale
(2, Fig. 2). To make a measurement on this scale follow the
same steps outlined above, but with these important
differences:
• The Semicircular Position Angle Scale reads from 0° to
90° clockwise and counterclockwise. The clockwise
direction is for measurements being made through mirrorlens Cassegrain telescopes (
e.g.
, Schmidt-Cassegrain,
Maksutov-Cassegrain), or refractors where a diagonal
mirror/prism is being used. Translate the 90° mark on the
opposite side of the scale as 270°.
• The counterclockwise direction is for a Newtonian
reflecting telescope or a telescope without a diagonal
mirror/prism. In this case the 90° mark should be on the
“left” side of the scale. Translate the 90° mark on the
opposite side of the scale to 270°.
270
240
210
180
150
120
90
60
30
0
330
300
90
60
30
0
0 1020304050
30
60
90
Fig. 2: MA 12mm Astrometric Eyepiece Reticle. (1) Linear Diameter Scale, (2) Semicircular Position Angle Scale;
(3) 360° Position Angle Scale; (4) Double Crossline/Concentric Circle Guiding Scale.
3
2
1
4
- 2 -
If the object to be measured is “below” the east-west line, then
the entire reticle must be rotated 180° to position the object
within the Semicircular Position Angle Scale. Follow these
steps:
1. Place a star on the 90° mark on the Position Angle Scale
2. Release the thumbscrew of the eyepiece holder and
rotate the eyepiece until the same star is lined up on the
270° mark.
3. Tighten the thumbscrew to lock the eyepiece in
position.zWith the Semicircular Position Angle Scale
turned “upside-down” the scale markings should be
translated as shown:
• The Semicircular Position Angle Scale reads from 0° to
90° clockwise and counterclockwise. The clockwise
direction is for measurements being made through mirrorlens Cassegrain telescopes (
e.g.
, Schmidt-Cassegrain,
Maksutov-Cassegrain), or refractors where a diagonal
mirror/prism is being used. Translate the 0° mark as 180°.
The 90° mark on the “right” side is correct, and the
opposite side of the scale translates to 270°.
• The counterclockwise direction is for a Newtonian
reflecting telescope or a telescope without a diagonal
mirror/prism. Translate the 0° mark as 180°. The 90° mark
on the “left” side is correct, and the opposite side of the
scale translates to 270°.
Guiding the Telescope: The Double Crossline/Concentric
Circle Guiding Scale (4, Fig. 2) is specifically designed for
guiding on a star during an astrophotograph. The finest
astrophotographs have sharply focused stars that are perfectly
round. In order to achieve this level of quality in the final image,
constant monitoring of a “guide star” is required to make the
proper “drive corrections.”
The double crosslines and concentric circles of the Guiding
Scale allow for a single star or group of stars to be guided on
simultaneously. The eyepiece is normally used in an off-axis
guider or guide telescope.
To determine the image scale in arc-seconds of the Guiding
Scale, use the eight steps outlined in Determining Image
Scale, with these important differences:
• Line up the star to be timed so that it runs parallel with one
of the double crosslines.
• Start timing the star as it enters one edge of the large
concentric circle.
• Finish timing the star as it leaves the other edge of the
large concentric circle.
There are four concentric circles in the scale. Each is
progressively smaller: the first circle’s diameter is half the size
of the largest circle, then one fourth, and then one-tenth. After
determining the image scale in arc-seconds of the largest
circle, multiply by 0.5, 0.25, and 0.1 respectively to learn the
image scale of the smaller concentric circles.
Maintenance: Avoid cleaning the eyepiece optics: a little dust
on the surface of the eyepiece causes virtually no degradation
of image quality and should not be considered reason to clean
the lens. DO NOT disassemble the eyepiece to clean the
interior lens surfaces or the reticle.
When absolutely necessary, dust should be removed with
gentle strokes of a camel hair brush or blown off with an ear
syringe (available at any pharmacy). DO NOT use a
commercial photographic lens cleaner.
Organic materials (
e.g.,
fingerprints) on the eyepiece may be
removed with a solution of 3 parts distilled water to 1 part
isopropyl alcohol. One drop of biodegradable dishwashing
soap per pint of solution may also be added. Use soft, white
facial tissues and make short, gentle strokes. Change tissues
often.
CAUTION: Do not use scented or lotioned tissues or
damage could result to the optics.
The LED Illuminator (3, Fig. 1) contains batteries that must be
replaced occasionally. Use two (2) Duracell MS-76 photo
batteries or equivalent. To open the illuminator, grab both ends
of the illuminator and twist one end counterclockwise. Between
battery replacements clean the battery contacts with the
eraser-tip of a pencil.
If you have any questions regarding the use of the MA 12mm
Astrometric Eyepiece, please call Meade Customer Service at
(949) 451-1450. Customer Service hours are from 7:00 A.M. to
5:00 P.M. Pacific Time, Monday through Friday.
Battery Safety Instructions
• Always purchase the correct size (2 x 1.5V MS-76/LR44,
SR1154, SR44 ANSI, LR6 IEC, SR1154 IEC) and grade of
battery most suitable for the intended use.
• Replace all batteries of a set at the same time.
• Clean the battery contacts and also those of the device
prior to battery installation.
• Ensure the batteries are installed correctly with regard to
polarity (+ and -).
• Remove the batteries from any weather station which is not
to be used for an extended period of time.
• Remove used batteries promptly.
• Do not mix old batteries with new batteries.
• Do not mix alkaline, lithium, standard (Carbon Zinc), or
rechargeable (Nickel Cadmium) batteries.
Caution:
• If batteries or parts are swallowed, see a doctor immediately.
STANDARD WARRANTY INFORMATION
This product is warranted by Meade Instruments Corp. (MIC) to
be free of defects in materials and workmanship for a period of
ONE YEAR from date of original retail purchase in the U.S.A.
MIC will repair or replace the product, or part thereof, found
upon inspection by MIC to be defective, provided the defective
part or product is returned to MIC, freight prepaid, with proof of
purchase. This warranty applies to the original purchaser only
and is non-transferable. Meade products purchased outside
North America are not included in this warranty.
RGA Number Required: Prior to the return of any product or
part, a Return Goods Authorization (RGA) number must be
obtained by writing to Meade's Customer Service Department
or by calling 800-626-3233. Each returned part or product must
include a written statement detailing the nature of the claimed
defect, as well as the owner's name, address, phone number,
and a copy of the original sales invoice.
This warranty is not valid in cases where the product has been
abused or mishandled, where unauthorized repairs have been
attempted or performed, or where depreciation of the product is
due to normal wear-and-tear. MIC specifically disclaims
special, indirect, or consequential damages or lost profits,
which may result from a breach of this warranty. Any implied
warranties which cannot be disclaimed are hereby limited to a
term of one year from the date of purchase by the original retail
purchaser. This warranty gives you specific rights. You may
have other rights which vary from state to state.
MIC reserves the right to change product specifications or to
discontinue products without prior notice.
This warranty supersedes all previous Meade product
warranties.
- 3 -
Meade Instruments Corp.
27 Hubble, Irvine, California 92618 U.S.A. • (949) 451-1450
•
www.meade.com
©2011 All rights reserved. Specifications subject to change without notice.
Ver. 011311
- 4 -
Loading...